I used Merrill's Compost Tea a couple of years ago and my orchids did not perform well. I think a lot of the nitrogen in compost comes from urea and ammonia and orchids can't readily utilize it. For the past year I've been using fertilizers that get nitrogen from nitrate only and I've seen a big difference in growth rates. A study done by a university in Texas (it might have been Texas A&M) showed that orchids utilize nitrogen derived from nitrate much better than nitrogen derived from urea or ammonia. That study is sited in the 4 part series called 'Growing the Best Phalaenopsis'. You can find it online. In any case I don't feel that compost teas are effective when used alone. Maybe they could be alternated with a chemical fertilizer.

Actually, I have decided that the NPK of a blended fertilizer is not very usefull and in fact misleading since it ignores calcium and magnesium which are at least as important as nitrogen, phosphorous and potassium.

I think that one can blend a good fertilizer using only calcium ammonium nitrate (YaraLiva Calcinit), magnesium nitrate (Magnisal) and potassium dihydrogen phosphate (MKP).

First determine the ratio of calcium ammonium nitrate to magnesium nitrate that will give you your desired ratio of calcium to magnesium. This also determines the percentage of nitrogen. For example, a 2:1 ratio of calcium ammonium nitrate to magnesium nitrate gives you 4:1 calcium to magnesium ratio and an NPK of 14-0-0 (12.7% Ca, 3.2% Mg). Then add MKP to get the desired amount of phosphorous and potassium. For example, 2:1:0.25
blend of Calcinit, Magnisal and MKP gives:
NPK 13-4-2.7 (11.7% Ca, 3% Mg).

I will look for that. I find it curious that nitrate would be much superior to ammonia especially since plants convert nitrate to ammonia to be utilized.

You certainly have a much better understanding of the chemical makeup of fertilizer than I do. I agree that calcium and magnesium are important elements according to everything I've read. Unfortunately Magnesium and phosphorus compete with each other for uptake by the plant. I've been using a calcium/magnesium supplement by itself, twice a month on my orchids and they seem to be doing well.

Here is the article:
http://www.hrt.msu.edu/faculty/Runkl...sis_Part_2.pdf
"Results from a recently completed study at Texas A&M University suggest that fertilizers high in ammoniacal nitrogen are not desirablefor the best vegetative growth and flowering."
Who knows what that really means, I would have to see the actually paper to see what parameters they did or did not control.

And speaking of controlling parameters, as I have mentioned, K-lite is also low P. If people are seeing benficial results from K-lite maybe it is from the low P. I wonder if it is the high P levels in many fertilizers that cause problems by reducing the availablity of calcium, magnesium, iron and copper. Maybe a P-lite with low P but higher levels of K would be even better.

Also from the above referenced article:

"A recently completed study showed that phalaenopsis that did not receive adequate levels of potassium may
appear healthy for several months, producing a similar number and size of new leaves as those receiving adequate potassium. As soon as spiking has taken place and while the young inflorescences grow, the limited pool
of potassium in the leaves and roots is remobilized to support the reproductive growth and the lower leaves start to show symptoms of potassium deficiency. Although plants that were deficient of potassium produced flowers, a few lower leaves were lost. All phalaenopsis planted in a bark mix and lacking potassium eventually died."

Thanks for the info Tucker! I've decided not to go that route... At least for now!

Being that chemical engineering is why out of my league.... I will be of no help, BUT....... You should post a thread on Slippertalk and see what the folks on there say.

I know nothing about growing slipper orchids so I have stayed out of the conversations there.

Actually K-Lite is 12:1:1, but I have puzzled over that one myself, David, and feel that it's not necessarily just the ratio that's the issue.

I think there are several things going on: One is the mass applied. I remember when I volunteered feeding the orchids at what is now the Atlanta Botanical Gardens back in the mid-70's, the concentrations applied were easily 10x-20x what is considered normal now.

The second part is closely tied to that - the rate of nitrogen uptake by a plant is greater than that of the other ions, so just because you apply a solution of a certain ratio, it does not mean that the plant takes them up in that same ratio. A high concentration of applied nitrogen means a large uptake - likely at a larger percentage than it would be at lower concentrations. Conversely, if I have a 12-1-1, 30-10-10, or a 1-1-1, and mix the solution to 50 ppm N, then I would expect the plant to take up the same amount of nitrogen from each of the solutions; at the dilution rates those are, I doubt there are any ion-interaction interferences going on.

I will add that - and this is part of the basis for the "K-Lite" concept in the first place - plant metabolic rates are slow. Many of the minerals we apply are absorbed and stored, even though the levels far exceed what the plant needs physiologically. Some of those are mobile within the plant, so new tissues can be supplied by the internal stores if they are not provided from outside, while others are not, so must be constantly replenished. The gist of all of this being that some nutrient minerals - N, Ca, and Mg - appear to require a steady supply in appreciable quantities as they are used by the plant in relatively large quantities and/or are not mobile and transferable to newly-formed tissues. Pretty much everything else is used in very small amounts and/or is relocatable, so the demand is low.

Plants have nutrient pumps that take up as much phosphorus (among other ions) as they can, storing it in cell vacuoles, so there is no need for high levels - that's the basis of the MSU formulas. It is also known that potassium is stored by plants far in excess of its needs, and it also can interfere with the uptake of other ions. It also is preferentially trapped by potting media, potentially leading to more overdosing. The K-Lite fertilizer was designed to compensate for that, reducing the potassium level, thereby slowing the rate of buildup in both the plant and the medium.

I guess the bottom line is that we need to think of plant food as both an immediate "fix", and as a "long-term integration" process, and understand that the label formula is not representative of what is taken up - sort-of like a kid who has a meal on his plant, and eats his meatloaf, gobbles up a second helping of mashed potatoes, but picks at his Lima beans.

Yes, I meant to write "K-lite is 100-10-10" to compare it against the MiracleGrow 30-10-10. And actually it is 120-10-10 compared to MiracleGrow's 30-10-10. Or you could say that K-lite is 12-1-1 compared to 3-1-1 for MiracleGrow. So K-lite could also be called N-Extreme.

And, so as to not confuse anyone, while NPK is actually an expression of absolute percentages it can also be thought of as a ratio. For example, 1 gram of a 30-10-10 fertilizer diluted in a liter of water gives the exact same amounts and concentration of nitrogen, phosphorous and potassium as 2 grams of a 15-5-5 fertilizer dilluted in a liter of water.


The same argument could be applied be applied to potassium. But a little farther on you argue that "Plants have nutrient pumps that take up as much phosphorus (among other ions) as they can, storing it in cell vacuoles, so there is no need for high levels "
So that you have just argued that neither concentration or ratio is extremely important and I agree.
Yep, that is one of the points that I was making - calcium and magnesium availability are as important as that of nitrogen, phosphorous and potassium.

Yes, and given sufficient concentration in the nutrient media the plants can adjust those pumps to take up each nutrient in the amount needed. So again, over a reasonable range, ratio is not critically important.

So I wonder why the plant wastes energy doing this? Actually, I thought that the more correct statement is that scientists have not been able to explain why plants store so much potassium, not that it has been determined that the amounts are in great excess of need.

Yes, in huge, osmotically significant excess but as you said, "plants have nutrient pumps" and aren't these pumps selective.

Preferential to what? The humic acids and other chelating agents in potting media should much prefer the divalent alkali metals calcium and magnesium and other multivalent cations such as iron and copper. Besides, if something is strongly bound to the substrate then it is not readily availabe to the plants.

(Which brings up another topic that I will start another thread about - the extremely strong chelating agents that are being used to prepare plant trace element nutrients)

Again, as you have noted, plants have pumps that selectively absorb what is need if it is available in sufficient concentrations. But unlike a canine they will not gorge themselves on everything that is put in front of them.

Yes, that is my point and that is why I don't understand this belief that very low K ratios are important.

If anything, I think having phosphate and sulfate levels that are not to high is likely much more important than the potassium level. Sulfate and especially phosphate can form insoluble salts with calcium, magnesium, iron, and copper unless a suitably low pH is maintained.

So I think it likely that any beneficial efects of K-lite are due to the phosphorous ratio that was lowered as dramatically as that of potassium and that K-lite perhaps would be more properly named P-lite or N-extreme.